Basement membrane components synthesized and secreted by a murine teratocarcinoma-derived cell line are studied. One of the soluble collagenous components has been isolated and characterized. It has an apparent molecular weight of 190,000 estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The posttranslational features, amino acid compositions and cyanogen bromide peptide pattern of this collagen strongly suggests that it is a Type IV collagen of basement membrane. The studies of the immunological relationship of this collagen to one other murine Type IV collagen isolated from an EHS sarcoma is in progress. The structural relationship of this collagen to other collagenous and non-collagenous proteins in the basement membrane will be studied.